The present invention relates generally to a modular connection capable of supporting PCI (Peripheral Component Interconnect) and PCI Express (PCIe) interfaces, and more specifically to removable a radio slot for a wireless local area network (WLAN) access point (AP).
A typical access point (AP) can employ a removable radio slot to enable it to be quickly and easily updated. For example, a chipset can be developed for to implement an 802.11 standard for the AP. The chipset is mounted on a removable card, such as a PCI card that is plugged into the access point. As changes to the standard occur, the AP can be updated by merely replacing the removable card in the AP with a removable card having a new chipset.
In the past, changing the removable card has not been a problem because 802.11 chipsets have been employed on cards using standard off the shelf PCI connectors (e.g., Cardbus, MPCI, PC104+). However, future 802.11 chipsets will utilize PCI Express (PCIe) connections due to the fact that laptops, and other small computer devices, will abandon the Cardbus interface in favor of the PCIe interface. Because of the uncertainty of exactly when the change from Cardbus to PCIe will occur, it is desirable that a modular AP have both PCI and PCIe connections. If separate, standard MCPI/Cardbus and PCI Express card interfaces are both installed on an AP, then the physical size of the AP will be larger than desired.
Thus, it would be desirable for an AP, or any other computing device, to be able to support the Cardbus PCI interface and the PCI Express interface using only one connector. However, the connector would have to be designed to overcome incompatibilities between the PCI and PCI express interfaces as will be explained hereinbelow.
The PCI bus was originally developed as a local bus expansion slot for the Personal Computer and was coined the PCI Local Bus. The specification started as an add-on to the ISA form factor with the PCI bus requiring its own connectors. The PCI spec defines Electrical requirements for the interface. No bus terminations are specified, the bus relies on signal reflection to achieve level threshold. The first Desk Top version of the PCI bus ran at 33 MHz with a 32 bit bus (133 MBps), the current Desk Top version runs at 66 MHz with a 64 bit bus. The Laptop version, (Mini-PCI) operates at 33 MHz with a 32 bit bus. The PCI bus operates either synchronously or asynchronously at the motherboard's bus rate. While operating asynchronously, the bus will operate at any frequency, e.g., from 66 MHz down to (and including) 0 Hz. Flow control is added to allow the bus to operate with slower devices on the bus, allowing the bus to operate at their speed. There are three card configurations for the Mini PCI bus, Type 1, Type II and Type III. Type I and Type II use a 100 pin connector, while Type III uses a 124 pin connector.
By contrast, PCI Express uses a pair of LVDS (Low Voltage Differential Signal) drivers and receivers and is not compatible with the legacy PCI bus, which does not use differential transceivers. The PCI Express bus uses two low-voltage differential signal pairs at 2.5 Gb/s in each direction, one pair for transmit, and one pair for receive. The differential trace impedance is defined as 100 ohms, ±15%. Each pair is capacitive coupled at the receiver. PCI Express supports 1×[2.5 Gbps], 2×, 4×, 8×, 12×, 16×, and 32× bus widths [transmit/receive pairs].